In satellite communication systems, there is a need for highly efficient wideband microwave amplifier systems suitable for use in communications systems. This is especially true where power and available energy are limited. Accordingly, a premium is placed on amplifier efficiency. Various apparatus are available for amplifying signals. In communication systems which involve the amplification and transmission of modulated signals, many modulated signals contain information in the amplitude envelope and the phase of the signal, a premium is placed on the ability to create a high fidelity reproduction of the signal. In particular, it is very desirable for an amplifier to exhibit very low amplitude distortion and very low phase distortion. Low distortion allows for clearer and more reliable communications. High efficiency allows for operate longer battery life and reduced power consumption.
One method of achieving increased efficiency is to use envelope elimination and restoration (EER)-type amplifiers. One problem with EER-type amplifiers is that the available bandwidth of the amplifier is limited to approximately one-fifth of the pulse width modulator bandwidth used in these EER-type amplifiers. This has relegated the use of EER-type amplifiers to systems with voice channel bandwidths. Recent advances in modulator performance have pushed the bandwidth achievable by EER-type amplifiers up to several hundred kilohertz. This is far less than the bandwidth required for communication systems, especially cellular and satellite communication systems that transmit and receive multicarrier wideband signals at microwave frequencies. For modern satellite communication systems and future satellite communication systems, bandwidths of several hundred megahertz up to several gigaHertz are desirable.
Thus, what is needed is an improved wideband microwave communication system, that is highly efficient. What is also needed is a highly efficient method of amplifying wideband multicarrier signals suitable for satellite communication systems.